Solar module having reflector between cells

ABSTRACT

A photovoltaic module comprising an array of electrically interconnected photovoltaic cells disposed in a planar and mutually spaced relationship between a light-transparent front cover member in sheet form and a back sheet structure is provided with a novel light-reflecting means disposed between adjacent cells for reflecting light falling in the areas between cells back toward said transparent cover member for further internal reflection onto the solar cells. The light-reflecting comprises a flexible plastic film that has been embossed so as to have a plurality of small V-shaped grooves in its front surface, and a thin light-reflecting coating on said front surface, the portions of said coating along the sides of said grooves forming light-reflecting facets, said grooves being formed so that said facets will reflect light impinging thereon back into said transparent cover sheet with an angle of incidence greater than the critical angle, whereby substantially all of the reflected light will be internally reflected from said cover sheet back to said solar modules, thereby increasing the current output of the module.

This invention was made under Department of Energy Subcontract No.NERL-ZAF-6-14271-13.

FIELD OF THE INVENTION

This invention relates to an improved solar cell module having reflectormeans designed to utilize light impinging on areas between the cellswhich would normally not be utilized in photoelectric conversion,thereby increasing the power output of the cell.

BACKGROUND OF THE INVENTION

Photovoltaic solar cells for directly converting radiant energy from thesun into electrical energy are well known. The manufacture ofphotovoltaic solar cells involves provision of flat semiconductorsubstrates having a shallow p-n junction adjacent one surface thereof(commonly called the "front surface"). Such substrates are oftenreferred to as "solar cell wafers". A typical solar cell wafer may takethe form of a rectangular EFG-grown polycrystalline silicon substrate ofp-type conductivity having a thickness in the range of 0.010 to 0.018inches and a p-n junction located about 0.3-0.5 microns from its frontsurface. Circular or square single crystal silicon substrates andrectangular cast polycrystalline silicon substrates also are commonlyused to make solar cells. The solar cell wafers are converted tofinished solar cells by providing them with electrical contacts(sometimes referred to as "electrodes") on both the front and rear sidesof the semiconductor substrate, so as to permit recovery of anelectrical current from the cells when they are exposed to solarradiation. These contacts are typically made of aluminum, silver, nickelor another metal or metal alloy. A common preferred arrangement is toprovide silicon solar cells with rear contacts made of aluminum andfront contacts made of silver. The contact on the front surface of thecell is generally in the form of a grid, comprising an array of narrowfingers and at least one elongate bus (commonly called a "bus bar") thatintersects the fingers. The width and number of the fingers and bus barsare selected so as to maximize the output current.

Further, to improve the conversion efficiency of the cell, it isaccepted practice to form on the front surfaces of the solar cells anelectrically non-conducting anti-reflection ("AR") coating that istransparent to solar radiation. In the case of silicon solar cells, theAR coating is often made of silicon nitride or an oxide of silicon ortitanium. Typically the AR coating is about 800 Angstroms thick. The ARcoating overlies and is bonded to those areas of the front surface ofthe cell that are not covered by the front contact, except that at leasta portion of the front contact (usually a bus bar) is not covered withthe AR coating, so as to permit making a soldered connection to thatcontact.

Photovoltaic solar cells (e.g., silicon solar cells) are relativelysmall in size, typically measuring 2-4 inches on a side in the case ofcells made from rectangular EFG-grown substrates, with the result thattheir power output also is small. Hence, industry practice is to combinea plurality of cells so as to form a physically integrated module with acorrespondingly greater power output. Several solar modules may beconnected together to form a larger array with a correspondingly greaterpower output.

The usual practice is to form a module from two or more "strings" ofsolar cells, with each string consisting of a plurality of cellsarranged in a straight row and electrically connected in series, and theseveral strings being arranged physically in parallel with one anotherso as to form an array of cells arranged in parallel rows and columnswith spaces between adjacent cells. The several strings are electricallyconnected to one another in a selected parallel and/or series electricalcircuit arrangement, according to voltage and current requirements. Acommon practice is to use solder coated copper wire, preferably in theform of a flat ribbon, to interconnect a plurality of cells in a string,with each ribbon being soldered to the front or back contact of aparticular cell, e.g., by means of a suitable solder paste.

For various reasons including convenience of manufacture and assembly,cost control, and protection of the individual cells and theirinterconnections, it has been common practice for such modules to havelaminated structures. These laminated structures consist of front andback protective sheets, with at least the front sheet serving as a coverand being made of clear glass or a suitable plastic material that istransparent to solar radiation, and the back sheet serving as a supportfor the cells and being made of the same or a different material as thefront sheet. Disposed between the front and back sheets so as to form asandwich arrangement are the solar cells and a light-transparent polymermaterial that encapsulates the solar cells and is also bonded to thefront and back sheets so as to physically seal off the cells. Thelaminated sandwich-style structure is designed to mechanically supportthe cells and also to protect the cells against damage due toenvironmental factors such as wind, snow, rain, ice, and solarradiation. The laminated structure typically is fitted into a metalframe which provides mechanical strength for the module, and facilitatescombining it with other modules so as to form a larger array or solarpanel that can be mounted to a support that is arranged to hold thearray of cells at the proper angle to maximize reception of solarradiation.

The art of making solar cells and combining them to make laminatedmodules is exemplified by the following U.S. Pat. Nos.: 4,751,191 (R. C.Gonsiorawski et al.); 5,074,920 (R. C. Gonsiorawski et al.), 5,118,362(D. A. St. Angelo et al.); 5,178,685 (J. T. Borenstein et al.);5,320,684 (J. Amick et al); and 5,478,402 (J. I. Hanoka). The teachingsof those patents are incorporated herein by reference thereto.

Unfortunately, when a plurality of cells are arrayed in a module, thetotal active surface area of the array (i.e., the active area of thefront faces of the solar cells) is less than the total area exposed toradiation via the transparent front protective sheet. For the most partthis is due to the fact that adjacent cells do not touch each other andalso the cells at the periphery of the array may not extend fully to theouter edges of the front protective sheet. Consequently less than all ofthe solar radiation which is received by the module impinges on activesolar cell areas, with the remainder of the received solar radiationimpinging on any inactive areas that lie between the cells or border theentire array of cells.

As noted in U.S. Pat. No. 4,235,643, issued Nov. 25, 1980 to James A.Amick for "Solar Cell Module", a number of techniques have been proposedfor increasing the efficiency and effectiveness of solar cell modules byconcentrating incident solar radiation onto active cell areas. Forexample, U.S. Pat. No. 2,904,612 describes a reflector-type device inwhich the land areas between the circular solar calls consistessentially of inverted intersecting frustums of cones circumscribingthe cells. Another technique employed to enhance solar cell moduleoutput is the use of lenses. Thus U.S. Pat. No. 3,018,313 describes asolar cell module which has an array of lenses covering the module so asto concentrate the light impinging on the cover of the solar cell arrayto converge downwardly toward the active solar cell area. In U.S. Pat.No. 4,053,327, yet another light focusing arrangement is describedwherein the cover of a solar cell module comprises a plurality ofconverging lenses arranged so as to direct the light incident on themodule so that it does not fall on the grid lines of the front electrodeof the solar cells in the array.

The Amick patent discloses an improvement over such prior efforts whichcomprises providing between adjacent cells an optical medium having aplurality of light-reflective facets that are angularly disposed so asto define a plurality of grooves having a depth in the range of 0.001"to 0.025", with the angle at the vertex formed by two mutuallyconverging facets being between 110° and 130°, preferably about 120°,with the result that light impinging on those facets will be reflectedback into the transparent front cover member at an angle φ greater thanthe critical angle, and then reflected again internally from the frontsurface of the cover member so as to impinge on the solar cells. Theterm "critical angle" refers to the largest value which the angle ofincidence may have for a ray of light passing from a more dense opticalmedium to a less dense optical medium. If the angle of incidence φexceeds the critical angle, the ray of light will not enter the lessdense medium (e.g, air) but will be totally internally reflected backinto the denser medium (e.g., the transparent cover sheet).

Amick U.S. Pat. No. 4,235,643 suggests (in column 4) that the facetedregion is substantially coplanar with the solar cells and preferably thevertical height of a facet will be equal to the thickness of the solarcell. In column 5 of the Amick patent it is stated that the grooves aremachined or molded in the optical medium.

Further information about the Amick invention is provided by thetechnical paper published by James A. Amick and William T. Kurth,"V-Groove Faceted Reflector For Enhanced Module Output", pp. 1376-1381,Record of IEEE Photovoltaic Specialists Conference--1981. In saidarticle, the authors disclose that the faceted reflector was made ofacrylic plastic and had a thin aluminum reflecting layer, with therepeat spacing (peak-to-peak spacing) of the facets being 0.070 inches.

However, the Amick reflector invention was not a commercial success. Aprimary limitation of the Amick invention was the inability to provide asatisfactory reflector medium at an acceptable cost.

Consequently, notwithstanding the advantages made in the recent years inincreasing the energy conversion efficiency of solar cells, there stillremains a very definite need for improving the ability of a solar cellmodule to capture and use available light energy and, more importantly,do so using a reflector medium that is relatively inexpensive tomanufacture and is easy to use.

OBJECTS AND SUMMARY OF THE INVENTION

A primary object of the present invention is to provide an improvedphotovoltaic solar cell module having novel reflector means forincreasing its power output.

Another object of the present invention is to provide an improved solarcell module comprising a plurality of solar cells arrayed in rows andcolumns between first and second support sheets, at least one of saidsheets being transparent to solar radiation, and novel flexiblereflector means disposed between said cells for increasing the amount ofradiation received by said cells through said transparent sheet.

Still another object is to provide a module of the type described thatcomprises one or more concentrator members in the form of athermoplastic film having a plurality of parallel grooves coated with alight-reflecting coating.

Another object is to provide a method of improving a solar module byincorporation therein of a novel solar energy reflector that operates soas to cause an increase the module's output current.

A further object is to provide an improved method of manufacturing asolar module.

These and other objects and advantages of the invention are achieved byproviding a novel photovoltaic module comprising an array ofelectrically interconnected photovoltaic cells disposed in a planar andmutually spaced relationship between a transparent front planar covermember in sheet form and a back support structure, with at least saidfront cover member being transparent to solar radiation, and a novellight-reflecting means disposed between adjacent cells for reflectinglight falling in the area between cells back toward said transparentcover member for further internal reflection onto the solar cells. Morespecifically, the solar cell module of the present invention comprises aplurality of mutually-spaced solar cells arrayed in a planar arrangementof rows and columns on a planar surface of the back sheet structure,with areas of said planar surface between the solar cells being coveredby a novel optically-reflective textured sheet material having aplurality of facets disposed in a predetermined angular relationshipwith respect to said cover member and each other, so that lightimpinging thereon through the front cover member will be reflectedupwardly back to the transparent cover member and then backwards towardactive areas of the cells. In accordance with this invention, theoptically reflective textured sheet material has a thicknesssubstantially less than the thickness of the solar cells and comprises(1) a substrate in the form of a thin and flexible thermoplastic filmthat has been embossed so as have a plurality of substantiallyflat-sided grooves of predetermined configuration, and (2) alight-reflecting coating on said substrate in the form of a metallicfilm (or a reflective film comprised of multiple dielectric layers, asfurther described hereinafter) that extends along said grooves and formsa plurality of discrete light-reflecting facets, said grooves having ageometry such that incident light normal to the solar cell module willbe reflected from said facets back into said transparent planar covermember and the angle of incidence of such reflected lighter at saidtransparent cover member will be greater than the critical angle,whereby substantially all of said reflected light will be directed byfurther reflection from said transparent cover member back to said solarcells, thereby increasing the power output of the module. Preferably thelight-reflecting coating is a thin film of a metal having a highreflectivity, e.g., silver and aluminum.

In one preferred embodiment the optically reflective sheet material isformed with grooves running in a single direction, but pieces of saidmaterial are positioned in the spaces between cells so that the groovesextend in one direction between rows of cells and in a differentdirection between columns of said cells. Another embodiment ischaracterized by having (1) a sheet of said optically reflectivematerial, with grooves all running parallel to one another, underlyingall of the solar cells and extending across the spaces between thecells, and (2) strips of said same material disposed between rows (orcolumns) of said cells so that the grooves in said strips extend at aright angle to the grooves in said sheet underlying said cells. In otherembodiments the textured material is made or arranged with groovesrunning in at least two different directions. Other embodiments,features and advantages of the invention will be apparent from thefollowing specification and the drawings wherein like numerals are usedthroughout to identify like parts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a conventional solar cell module, with part ofthe transparent cover member broken away;

FIG. 2 is a fragmentary diagrammatic sectional view of a portion of themodule of FIG. 2;

FIG. 3 is a fragmentary side elevation on a greatly enlarged scale of apreferred form of textured reflective laminated film material providedaccording to the present invention;

FIG. 4 is a diagrammatic illustration of how the textured reflectivematerial of FIG. 3 is used in a solar cell module;

FIG. 5 is a diagrammatic illustration of one embodiment of the presentinvention;

FIG. 6 is a diagrammatic illustration of another embodiment of thepresent invention;

FIG. 7 is a fragmentary view of a portion of a preferred form of thereflective laminated film provided according to the invention; and

FIG. 8 illustrates another form of reflective laminated film materialaccording to this invention.

In the several drawings, the relative thicknesses of the plastic filmand metal layer that make up the flexible light-reflective laminatedmaterial are exaggerated in relation to the other solar modulecomponents solely for convenience of illustration.

FIGS. 1 and 2 illustrate a conventional solar cell module 2 comprising aplurality of rectangular solar cells 4. The kind of solar cells used inthe module may vary. Preferably, but not necessarily, the modulecomprises silicon solar cells. Although not shown, it is to beunderstood that each solar cell comprises a front contact on its frontsurface in the form of a grid comprising an array of narrow, elongateparallel fingers interconnected by one or more bus bars, and a rearcontact on its rear surface, with the cells made substantially asillustrated and described in said above-identified U.S. Pat. Nos.4,751,191, 5,074,920, 5,118,362, 5,178,683, 5,320,684 and 5,478,402. Themodule also comprises a back protector member in the form of a sheet orplate 6 that may be made of various materials and may be stiff orflexible. Preferably the back protector sheet 6 is an electricallyinsulating material such as glass, a plastic, a plastic reinforced withglass fibers or a wood particle board. A preferred back protector memberis Tedlar®. The solar cells are arranged in parallel rows and columnsand are interconnected by electrical leads 8 which usually are in theform of flat copper ribbons. The usual practice in making a solar moduleis to interconnect the cells in each row in series so as to formstrings, and then connect the strings in series or in parallel, or insome series/parallel combination, according to the voltage and currentrequirements of electrical system into which the module is to beinstalled. Referring to FIG. 2, adjacent cells in a string are connectedin series by soldering one end of a flexible copper ribbon 8 to the backelectrode of one solar cell and soldering the opposite end of the sameribbon to a bus bar of the front contact on the next succeeding solarcell.

Overlying the cells is a stiff or rigid, planar light-transmitting andelectrically non-conducting cover member 10 in sheet form that alsofunctions as part of the cell support structure. Cover member 10 has athickness in the range of about 1/8" to about 3/8", preferably at leastabout 1/4", and has an index of refraction between about 1.3 and 3.0. Byway of example, cover member 10 may be made of glass or a suitableplastic such as a polycarbonate or an acrylic polymer.

Interposed between back sheet 6 and transparent cover member 10 andsurrounding the cells 4 and their electrical connector ribbons 8 is anencapsulant 14 which is made of suitable light-transparent, electricallynon-conducting material. Preferably encapsulant 14 is the ethylene vinylacetate copolymer known in the trade as "EVA", or an ionomer. A commonpractice is to introduce the encapsulant in the form of discrete sheetsthat are positioned below and on top of the array of solar cells, withthose components in turn being sandwiched between the back sheet 6 andthe cover member 10. Subsequently that sandwich is heated under vacuum,causing the encapsulant sheets to become liquified enough to flow aroundand encapsulate the cells and simultaneously fill any voids in the spacebetween the front cover member and the rear support that may result fromevacuation of air. On cooling the liquified encapsulant solidifies andis cured in situ to form a transparent solid matrix that envelops thecells and fully fills the space between the back sheet 6 and covermember 10 that is not occupied by the mutually spaced cells and thecomponents that form their electrical interconnections. The encapsulantadheres to the front and back sheets 6 and 10 so as to form a laminatedsubassembly.

Regardless of how the laminated subassembly is made, it usually isprovided with and secured to a surrounding frame 16, with a sealant 18usually disposed between the frame and the edges of the laminatedsubassembly. The frame may be made of metal or molded of a suitablematerial such as an organic plastic or elastomer material. Although notshown, it is to be understood that a conventional module such as shownin FIGS. 1 and 2 also is provided with electrical terminals forconnecting the module to another module or directly into an electricalcircuit, with the terminals usually being affixed to the rear supportsheet 6.

The present invention improves upon the Amick invention by substitutinga less expensive but equally performing reflecting means for Amick'sreflecting means with its machined or molded grooves. For conveniencethe invention is described and illustrated hereinafter in the context ofadding a novel textured reflector material to the conventional modulestructure shown in FIGS. 1 and 2, so that the textured material extendsalong the spaces between adjacent cells and also any spaces borderingthe array of cells.

FIG. 3 is a side elevation of a portion of a preferred form of texturedmaterial 20 that is used as a reflector means according to the presentinvention. The reflector material is textured by the presence of groovesas hereinafter described so that it is capable of reflecting light whichnormally impinges on the land areas between and around the cells in themodule at an angle such that the reflected radiation, when it reachesthe front surface of the cover member, will be totally internallyreflected back down to the array of solar cells. The textured materialcomprises a substrate in the form of a thin and flexible thermoplasticfilm 22 that is coated on one side with a light reflecting metal film24. The substrate is formed with a plurality of contiguous V-shapedgrooves 26 each defined by a pair of flat mutually converging surfaces27A, 27B that extend at a predetermined angle to one another in therange of 110° to 130°, preferably about 120°, with the result that theportions 24A and 24B of the metal coating on those surfaces formlight-reflecting facets. Since the angle between said facets is between110° and 130°, each facet extends at an angle of between 25° and 35°relative to the plane of said cover member.

The textured material 20 is produced in several steps. First, the film22 that serves as the substrate is manufactured as a continuous orextended web having flat front and back surfaces, and that continuousweb is then wound onto a roll for subsequent processing, or it may bepassed directly to subsequent processing stages. The subsequentprocessing comprises first embossing the film so as to form the V-shapedgrooves on one side, and then metallizing the grooved surface of thefilm. Preferably, the embossing is accomplished by passing the filmbetween a pinch roller and an embossing roller, the pinch roller havinga smooth cylindrical surface and the embossing roller having a pluralityof contiguous V-shaped ridges on its cylindrical surface with the ridgesextending around the periphery of the embossing roller. The embossingroller ridges are reverse (negative) images of the desired V-shapedgrooves in shape and depth. The film is heated so that as it passesbetween the two rollers it is soft enough to be shaped by the ridges onthe embossing roller. The grooves formed by the ridges are fixed inshape on cooling of the film. After formation of grooves 26, the plasticfilm is subjected to a metallizing process wherein the adherent metalfilm 24 is formed. Preferably, but not necessarily, this is done by aconventional vapor deposition process on a continuous basis as a secondstage in a high speed machine that includes an embossing first stage andmeans for transporting the continuous plastic film through its variousstages at a relatively high speed. The metallized film is wound on aroll for subsequent use as a light reflector means as herein described.Subsequently pieces are cut from the rolled metallized film for use aslight reflector means according to the invention.

Still referring to FIG. 3, the substrate is made of a plastic filmmaterial which is thermoplastic and which may be transparent,translucent or opaque. For reasons of cost and ease of use, a readilyavailable plastic film is preferred for the substrate 22, with the filmbeing sufficiently flexible to allow it to be stored in roll form. Onesuitable substrate material is polyethylene terephthalate, one form ofwhich is sold as a transparent film wound in rolls under the trademarkMylar®. Other plastic films also may be used. By way of example but notlimitation, the substrate may be a film made of other polyesters or apolyolefin such as polyethylene or polypropylene. Still other plasticfilms will be obvious to persons skilled in the art.

It has been determined that a satisfactory flexible textured reflectorsheet can be made using as the substrate a plastic film having athickness in the range of 4 to 10 mils (0.004 to 0.010 inch). Preferablythe substrate has a thickness of about 5 mils. Currently aluminum ispreferred as the reflective metal coating for reason of cost, but silvermay become the preferred coating since its reflectivity is sufficientlyhigher than aluminum to offset the difference in cost. In this contextit should be noted that aluminum has a reflectivity of about 80-85%while silver has a reflectivity of 95-98%. The metal is applied in avery thin coating in the order of Angstrom units, preferably having athickness in the range of 300 Å to 1000 Å, more preferably between 300 Åto 500 Å. By way of example, in a substrate having a thickness of about0.005 inch and V-shaped grooves with an included angle between 110° and130°, the grooves have a depth of about 0.002 inch and a repeat(peak-to-peak) spacing of about 0.007 inch.

The textured material 20 is disposed so that it occupies the spaces("land areas") between cells in a module. Because of the above-describedgeometry of grooves 26, light reflected from one facet is not blocked byany adjacent facet and instead light reflected from the facets andpassing into the transparent cover member will strike the front face ofthe cover member at an angle exceeding the critical angle, with theresult that substantially all of the reflected light is reflectedinternally back toward the solar cells, thereby substantially improvingthe module's electrical current output.

FIG. 4 illustrates how the textured laminated reflector material of FIG.3 is used in a module. Essentially the laminated sheet material 20 isdisposed in the areas 30A between adjacent rows of cells and the areas30B between adjacent columns of cells, and also in the areas 30C and 30Dthat border the array of cells. The textured material is disposed sothat in FIG. 4, for example, the grooves 26 extend horizontally in theareas 30A and 30D and vertically in areas 30B 30C. For convenience andsimplicity, only some of the grooves 26 are shown in FIG. 4 and thenonly part of their full length. However, it is to be understood that thegrooves extend for the full expanse of the land areas 30A, 30B, 30C and30D.

FIG. 5 illustrates one way that the arrangement shown in FIG. 4 can beachieved. In this case, a sheet 20A of the laminated reflector filmmaterial of FIG. 3 is placed under the array of cells, the sheet beinglarge enough to protrude beyond the periphery of the array, with thegrooves of that sheet extending in the same direction in land areas 30A,30B and 30C. Then an additional length of the same laminated reflectorfilm material is cut into strips 20B with the grooves running lengthwiseof the strips, and those strips are then placed over sheet 20 in thoseportions of areas 30A that lie between adjacent areas 30B and alsobetween areas 30B and 30C, and the areas 30D between areas 30C so thatthe grooves of members 20A and 20B provide a pattern as shown in FIG. 4.More specifically, a plurality of grooves are disposed between andextend parallel to vertical columns of cells while additional groovesare disposed between and extend parallel to the cell rows. Thisarrangement has been found to be advantageous in that only one form oftexturized reflector sheet material is required to be used, while havingthe grooves between adjacent rows oriented at a right angle to thegrooves between columns improves the amount of light that is internallyreflected from the areas between the cells back onto the front surfacesof the cells.

FIG. 6 illustrates a second way to obtain a patterned groove arrangementas shown in FIG. 4 using a laminated plastic film as shown in FIG. 3. Inthis case, the laminated sheet 20A is omitted and instead the laminatedplastic film having parallel grooves running along its length is cutinto a plurality of strips 20B, each having the grooves 26 runninglengthwise, and one of those strips is placed in each of the land areas30A and 30D so that their grooves extend horizontally as viewed in FIG.4, and additional like strips (not shown) are placed in areascorresponding to land areas 30B and 30C of FIG. 41 so that their groovesextend vertically as seen in FIG. 4. It should be appreciated that atthe intersections of land areas 30B and 30C with land areas 30A and/or30D, the grooves may extend either horizontally or vertically.

FIG. 7 is a fragmentary plan view of a preferred form of laminatedplastic film reflector material 20C. It is to be understood thatmaterial 20C also comprises a plastic film that has grooves formed byembossing as above described and also a metal film covering andfollowing the contour of the grooves. However, in this case theembossing roll (not shown) is designed to emboss a rectangular patternof grooves 28 that have a cross-sectional shape like grooves 26, certainof the grooves 28A extending lengthwise in one direction and theremaining grooves 28B extending at a right angle to grooves 28A, therebyleaving rectangular flat areas 29 each of which is sized so that a solarcell 4 will fit in that area. The laminated film material can be madewide enough so that the number of rectangular areas 29 formed across itswidth is equal to the number of cells in a row or column of cells in anintended module, in which case the web of laminated film can be severedinto discrete pieces having areas 29 equal in number to the number ofcells in an intended module.

FIG. 8 shows another form of laminated plastic film 20D. In this casethe film is embossed with a herringbone pattern of grooves 32A and 32B.This material may be used in place of sheet 20A in which case strips 20Bmay be omitted from the embodiment of FIG. 5, or it may be cut intostrips and used in place of strips 20B in the embodiment of FIG. 6.

An example of the manufacture of modules incorporating the laminatedplastic film material provided by this invention is accomplishedaccording to the following method and the technique illustrated in FIG.6. An array of cells are disposed on the back sheet 6 over a sheet ofencapsulant such as EVA or ionomer. The cells are interconnected to oneanother and also to output terminals on the back sheet as previouslydescribed. Then pieces of said laminated plastic film material, cut intosuitable shapes, are positioned in the spaces between the cells asdescribed in connection with FIG. 6. Next another sheet of encapsulantis placed over the cells and covered by a transparent front cover sheetmade of glass or plastic. Finally the module is heated under vacuum tocause the two sheets of encapsulant to fuse to one another and to theexposed surface areas of the back sheet, the front cover, the cells andthe laminated plastic film material. This module is then available formounting in a frame for subsequent use.

Alternatively, the module may be assembled in reverse fashion, with thetransparent glass or plastic sheet serving as the support for the modulecomponents during module assembly. In this method a layer of encapsulantwould be placed over the transparent sheet with the cells placed facedown on this layer. A second relatively thin layer of encapsulant wouldbe laid over the rear of the cells, and a textured sheet as in FIG. 7laid face down over the second encapsulant sheet with its grooves facingdown. Then a third thin encapsulant sheet is placed over the texturedreflector sheet and that is covered by a back sheet made of glass. Thenthe foregoing sandwich is laminated under heat and vacuum as previouslydescribed.

The following demonstrates the amount of improvement provided by thisinvention. Ten cell coupons were made using EVA as the encapsulant and0.25 inch thick glass as the front cover sheet. Each coupon comprisedone solar cell measuring 100 mm. on each side. Each cell was surroundedby 4 strips of laminated reflector material, one strip along each sideof the cell, with the grooves running in one direction along twoopposite sides of the cell and at a second direction at a right angle tothe first direction along the other two sides of the cell, essentiallyin a pattern like that of FIG. 4. The laminated reflector materialconsisted of 0.005 inch thick Mylar® film having an aluminum coatingapproximately 400 Å thick on its top surface. The Mylar® film had beenembossed before being metallized, the embossing producing V-shapedgrooves having an included angle of about 120°, a depth of about 0.002inch and a repeat spacing of about 0.007 inch. Each strip of laminatedfilm measured about 25 mm. wide. These coupons, and another couponhaving no reflector material but with an opaque mask surrounding it,were tested by illuminating each cell with a solar simulator lightsource and measuring the short circuit current. The 10 coupons havingthe laminated reflecting plastic film showed improvements in outputpower ranging from 20.8 to 25.6% greater than the power output of thecell that did not have the novel reflecting medium. It has been foundalso that a like cell surrounded by a flat white surface showed anoutput power increase no better than about 10% greater than the cellhaving no reflecting medium.

The invention also includes the concept of replacing the reflectivemetal coating on the plastic film with a dielectric stack comprisingmultiple layers of inorganic materials such as SiO₂, and Si₃ N₄ arrangedso as to form a reflecting mirror. Dielectric mirrors are well known;see A. Scherer et al, "Reactive Sputter Deposition of High ReflectivityDielectric Mirror Stacks", J. Vac. Sci. Technol. (1993). Plastic filmwith dielectric mirror coatings are available commercially from variouscompanies.

The invention also contemplates installing the laminated reflectingmaterial consisting of a transparent plastic film substrate and a metalcoating on its grooved surface so that the metal coating is facing awayfrom the transparent cover sheet so as to avoid any possibility of themetal film short circuiting the cells.

The invention is not limited in its application to any particular kindof solar cell, or solar cell encapsulant or cover sheet or back sheet.The invention is susceptible of various modifications that will beobvious to persons of ordinary skill in the art.

What is claimed is:
 1. A solar cell module comprising:a supportstructure having a planar surface adapted to support an array of solarcells; a plurality of solar cells overlying said planar surface, saidcells having front and back surfaces with said back surfaces facing saidplanar surface, said cells being spaced from one another in an array ofrows and columns, whereby predetermined areas of said planar surface arefree of solar cells; a transparent cover member overlying and spacedfrom all of said solar cells; a light-reflecting medium overlying saidpredetermined areas of said planar surface, said light-reflecting mediumcomprising a flexible laminated sheet material in the form of a flexibleplastic film coated with a light-reflecting coating, said laminatedsheet material having a thickness less than the thickness of said cells,said plastic film being textured by embossing so that said laminatedsheet material has a plurality of light-reflecting facets each having apredetermined angular relationship with respect to said cover member andsaid planar surface, whereby light impinging on said facets is reflectedback to said transparent cover member at an angle relative to said covermember which is greater than the critical angle, whereby said reflectedlight is internally reflected by said cover member back toward saidsolar cells.
 2. The module of claim 1 wherein said laminated sheetmaterial has a plurality of parallel V-shaped grooves with said facetsconstituting the sides of said grooves.
 3. The module of claim 2 whereinsaid grooves have a depth less than the thickness of said plastic film.4. The module of claim 2 wherein each facet extends at an angle between25 and 35 degrees relative to the plane of said cover member.
 5. Themodule of claim 2 wherein said plastic film has a thickness in the rangeof 0.004 inch to 0.010 inch, and said grooves have a depth ofapproximately 0.002 inch.
 6. The module of claim 5 wherein said grooveshave a repeat spacing of about 0.007 inch.
 7. The module of claim 2wherein said plastic film has a thickness in the range of 0.004 inch to0.010 inch and said grooves have a repeat spacing of about 0.007 inch.8. The module of claim 2 wherein said light-reflecting medium comprisesseveral pieces of said laminated sheet material disposed so that saidgrooves extend in a first direction between adjacent rows of cells and asecond direction between adjacent columns of cells.
 9. The module ofclaim 2 wherein said flexible laminated sheet material has a firstplurality of grooves extending parallel to one another and a secondplurality of grooves extending parallel to one another but at an angleto said first plurality of grooves.
 10. The module of claim 9 whereinsaid solar cells have a rectangular shape, and said first and secondpluralities of grooves are arranged to define a plurality of rectangularopen areas sized to accommodate said solar cells, and said laminatedsheet material is disposed so that each of said open areas is covered bya solar cell and said grooves are located in spaces between solar cells.11. The module of claim 2 wherein said grooves have a depth ofapproximately 0.002 inch.
 12. The module of claim 1 wherein saidlight-reflecting medium comprises a film of a flexible thermoplasticorganic polymer and said coating is made of aluminum or silver.
 13. Themodule of claim 12 wherein said organic polymer is a polyethyleneterephthalate material.
 14. The module of claim 12 wherein said coatingis made of aluminum or silver.
 15. The module of claim 12 wherein saidcoating is made of silver.
 16. The module of claim 12 wherein saidcoating is made of aluminum.
 17. The module of claim 1 wherein saidcells and said light-reflecting medium are encapsulated in a lighttransmitting polymer material that extends to and is bonded to saidcover member and said planar surface of said support structure, withsaid light transmitting polymer being engaged with and bonded to saidlight-reflecting medium.
 18. The module of claim 1 wherein said flexiblelaminated sheet material is interposed between said cells and saidplanar surface of said support structure, and further wherein said cellsand said laminated sheet material are encapsulated in a lighttransmitting polymer material that extends to and is bonded to saidcover member and said planar surface of said support structure.
 19. Themodule of claim 18 wherein said plastic film has a plurality of parallelV-shaped grooves with said facets constituting the sides of saidgrooves, and further wherein said grooves have a depth of approximately0.002 inch.
 20. In a solar cell module having a plurality ofelectrically interconnected solar cells arrayed in rows and columns on aplanar surface of a support structure with at least some of said cellsbeing spaced from one another so that selected areas of said planarsurface are not covered by said cells, a light-transparent cover memberoverlying and spaced from said cells, and a light-transparent solidmedium overlying and encapsulating said cells, said light-transparentsolid medium being bonded to said cover member, the improvementcomprising:a flexible laminated light-reflecting medium overlying saidplanar surface in said selected areas and encapsulated by saidlight-transparent solid medium, said light-reflecting medium comprisinga flexible plastic film that has a front surface facing said covermember and a rear surface and which has been embossed at said frontsurface so that said front surface defines a plurality of V-shapedgrooves each having an included angle between 110° and 130°, and areflective film covering and bonded to said front surface, saidreflective film conforming to the shape of and being coextensive withsaid grooves whereby portions of said reflective film covering the sidesof said grooves form a plurality of light reflective facets that arebonded to said light-transparent solid medium, each of said facetsextending at an angle to said cover member such that light impinging onsaid facets will be reflected upwardly through said light-transparentsolid material into said transparent cover member and then downwardlythrough said light-transparent sold material toward said cells.
 21. Theimprovement of claim 20 wherein said grooves each have a depth ofapproximately 0.002 inch.
 22. The improvement of claim 20 wherein thegeometry of said grooves is such that incident light normal to the solarcell module which impinges on said light-reflecting medium will bereflected by said reflective facets back through said light-transparentsolid medium to said cover member at an angle to said cover member whichis greater than the critical angle.
 23. The improvement of claim 20wherein said film has a thickness in the range of 0.004 inch to 0.010inch.
 24. The improvement of claim 20 wherein said grooves have a repeatspacing of approximately 0.007 inch.
 25. A solar cell modulecomprising:a structure adapted for supporting an array of solar cells; aplurality of solar cells arrayed on said support structure so thatselected areas of said support structure are exposed; a light-reflectingmedium disposed in said selected areas so as to extend into proximitywith each adjacent cell bordering said areas; a light-transparent covermember overlying and spaced from said solar cells, said cover memberbeing parallel to said support structure and the planes of said solarcells, said cover member having an index of refraction between 1.3 and3.0; and a light-transparent optical medium covering said cells and saidlight-reflecting medium, said light transparent optical medium extendingto and being bonded to said cover sheet; said light-reflecting mediumcomprising a flexible laminated sheet material in the form of a flexibleplastic film with a thickness between 0.004" and 0.010" that has frontand rear surfaces and has been embossed so that said front surface ischaracterized by a plurality of V-shaped grooves, and a light-reflectingmetallic coating covering said front surface of said plastic film,portions of said metallic coating on the areas of said front surfacethat define said plurality of grooves forming light-reflecting facets,said grooves having a geometry such that light passing through saidlight transparent optical medium and impinging on said light-reflectingfacets will be reflected upwardly through said optical medium to saidcover member and thereafter internally reflected downwardly from saidcover member through said light transparent optical medium to said solarcells.
 26. A module according to claim 25 wherein said cells have arectangular shape and are arranged in rows and columns, and furtherwherein said light-reflecting medium comprises strips of said flexiblelaminated sheet material disposed between adjacent rows of cells andalso between adjacent rows of cells.
 27. A method of increasing theoutput current of a given solar cell module having a back sheet, atransparent front cover sheet, and a plurality of solar cells arrayed onsaid back sheet between said back sheet and said cover sheet, said arrayof cells defining land areas therebetween, said method comprising:(1)placing in said land areas a flexible light-reflecting laminated sheetmaterial comprising a flexible plastic film having front and rearsurfaces and a thin reflective coating on said front surface facing saidcover sheet, said plastic film having a plurality of V-shaped groovesembossed in said front surface, portions of said reflective coatingalong said grooves forming flat light-reflecting facets with said facetsoriented as an angle of between 25 and 35 degrees to said cover sheet;and (2) reflecting solar radiation impinging on said facets via saidtransparent cover sheet back into said transparent cover sheet so thatsaid reflected solar radiation will be reflected internally from saidcover member downwardly toward said solar cells, whereby light impingingon said facets is directed onto said solar cells and thereby increasesthe output current of said solar cell module.
 28. A method of increasingthe output current of a given solar cell module having a back sheet, atransparent front cover sheet, and a plurality of solar cells arrayed onsaid back sheet between said back sheet and said cover sheet, said arrayof cells defining land areas therebetween, said methodcomprising:providing an extended length web of a flexible plastic filmhaving flat front and back surfaces and a thickness in the range of0.004 to 0.010 inch; embossing said front surface of said plastic filmso as to form parallel V-shaped grooves therein each having a depth ofapproximately 0.002 inch and an included angle in the range of 110° to130°; coating said embossed front surface of said plastic film with areflective coating having a thickness of about 1000 Angstroms or less soas to form a laminated film material comprising said plastic film andsaid coating, with portions of said coating along said grooves forminglight-reflecting facets; severing at least one selected length of saidlaminated film material from said web and placing said at least oneselected length in said land areas between said back sheet and saidfront cover sheet so that the widest portions of said grooves face saidcover sheet; and reflecting solar radiation impinging on said facets viasaid transparent cover sheet back into said transparent cover sheet sothat said reflected solar radiation will be reflected internally fromsaid cover member downwardly toward said solar cells, whereby lightimpinging on said facets is directed onto said solar cells and therebyincreases the output current of said solar cell module.
 29. The methodof claim 28 wherein said cells are rectangular in shape and are arrangedin rows and columns, and further wherein several lengths of saidlaminated film material severed from said web are placed in said landareas so that between said rows said grooves run parallel to said rowsand between said columns said grooves run parallel to said columns. 30.A method of manufacturing a solar cell module comprising the followingsteps:providing an extended length web of a flexible plastic film havingflat front and back surfaces and a thickness in the range of 0.004 to0.010 inch; embossing said front surface of said plastic film so as toform contiguous parallel V-shaped grooves therein, with each groovehaving an included angle in cross section in the range of 110 to 130degrees; coating said embossed front surface of said plastic film with areflective coating having a thickness of about 1000 Angstroms or less soas to form a laminated film material comprising said plastic film andsaid reflective coating, with portions of said reflective coating alongsaid grooves forming light-reflecting facets; severing at least oneselected length of said laminated film material from said web; providinga back sheet, a transparent front cover sheet, and a plurality of solarcells arrayed on said back sheet with land areas between said cells;placing said at least one selected length of said laminated filmmaterial in said land areas in overlying relation with said back sheet,with the widest portions of said grooves facing away from said backsheet; and sealing said cells and said laminated film material to saidcover sheet and said back sheet with a polymeric light-transmittingmedium that is interposed between and bonded to said cover sheet andsaid back sheet and encapsulates said cells and said at least oneselected length of said laminated film material, whereby to form asealed solar module.
 31. The method of claim 30 wherein said reflectivecoating is a metal film or comprises a plurality of dielectric films.32. The method of claim 30 wherein said grooves have a depth ofapproximately 0.002 inch.
 33. A method of manufacturing a solar cellmodule comprising the following steps:providing an extended length webof a laminated film material that comprises (a) a flexible plastic filmhaving flat front and back surfaces and a thickness in the range of0.004 to 0.010 inch, with said front surface of said plastic filmembossed so as to form contiguous parallel V-shaped grooves therein witheach groove having in cross-section an included angle in the range of110 to 130 degrees, and (b) a reflective coating on said front surfacehaving a thickness of about 1000 Angstroms or less, with portions ofsaid reflective coating along said grooves forming light-reflectingfacets; severing at least one selected length of said laminated filmmaterial from said web; providing a back sheet, a transparent frontcover sheet, and a plurality of solar cells arrayed on said back sheetwith land areas between said cells; placing said at least one selectedlength of said laminated film material in said land areas in overlyingrelation with said back sheet, with the widest portions of said groovesfacing away from said back sheet; and sealing said cells and saidlaminated film material to said cover sheet and said back sheet with apolymeric light-transmitting medium that is interposed between andbonded to said cover sheet and said back sheet and encapsulates saidcells and said at least one selected length of said laminated filmmaterial, whereby to form a sealed solar module.
 34. A solar cell modulecomprising:a support structure having a planar surface adapted tosupport an array of solar cells; a plurality of solar cells arrayed onsaid planar surface, said cells having front and back surfaces with saidback surfaces facing said planar surface, said cells being spaced fromone another in an array of rows and columns, whereby predetermined areasof said planar surface are free of solar cells; a transparent covermember overlying and spaced from all of said solar cells; alight-reflecting medium overlying said predetermined areas of saidplanar surface, said light-reflecting medium comprising a flexiblelaminated sheet material in the form of a flexible plastic film having athickness in the range of 0.004 inch to 0.010 inch and coated with alight-reflecting coating having a thickness substantially less than thethickness of said plastic film, said plastic film being textured byembossing so that said laminated sheet material has a plurality ofV-shaped grooves each having an included angle in the range of 110° to130° with the sides of said grooves functioning as light-reflectingfacets, whereby light impinging on said facets is reflected back to saidtransparent cover member at an angle relative to said cover member whichis greater than the critical angle, whereby said reflected light isinternally reflected by said cover member back toward said solar cells;and a light-transmitting polymer material disposed between and bonded tosaid cover member and said support structure in encapsulating relationwith said solar cells and said light-reflecting medium.
 35. A solar cellmodule according to claim 34 wherein said light-transmitting polymermaterial is EVA or an ionomer.
 36. A solar cell according to claim 35wherein said plastic film is a polyester or a polyolefin.